Loudspeakers

ABSTRACT

A loudspeaker is provided in which a thin surround is employed for the speaker cone of impervious foam material, the surround being characterized by omni-directional elastic tension and being secured between the cone and the support.

United States Patent 1 1 A 1111 3,767,004

Liebscher Oct. 23, 1973 [54] LOUDSPEAKERS 3,093,207 6 1963 Bozak 181/32 R [761 lnvemo" Arthur Liebscherzsz wyncote 3,436,494 4x96; 3221? Road,.lenkintowp, Pa. 190 4 [22] Filed: 1971 Primary Examiner-Stephen J. Tomsky [2i] Appl. No.: 126,330 Att0rneyZachary T. Wobensmith Related [1.8. Application Data [63] Continuation-impart of Ser. No. 864,322, Oct. 7,

1969, abandoned.

[57] ABSTRACT A loudspeaker is provided in which a thin surround is [52] US. Cl. 181/32 R, l8l/DIG. l employed for the Speaker cone of impervious foam [51] Int. Cl. Gl0k 13/00, H04r 7/00 material, the Surround being characterized by omni [58] Field of Search l8l/32 R, DIG. l directional elastic tension and being Secured between d t. [56] References Cited the cone an the Supper UNITED STATES PATENTS 2 Chims, 1 Drawing Figure 2,905,260 9/1959 Williams 181/32 R f T30 E, 32 429 9 Jr 28 /8 T LOUDSPEAKERS CROSS REFERENCE TO RELATED APPLICATION This application is a continuation-in-part of my prior application for Letters Patent for Loudspeaker filed Oct. 7, 1969, Ser. No. 864,322, now abandoned.

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to loudspeakers and more particularly to an improved speaker cone surround.

2. Description of the Prior Art Various mountings for the periphery of the cone or diaphragm of a loud speaker have heretofore been proposed but none of these has proven wholly satisfactory. Impregnated fiber cones employing edges of rolled fabric or sheet rubber surrounds, and polyurethane foam surrounds have been used but many of these age, crack and fail over a period of use and of time. Sheet rubber as a surround exerts excessive stresses, while polyurethane foam lacks stretchability and is not omnidirectional in tension. Such cone support'mountings by their limit of elasticity or excursion deform the cone to cause distortion of reproduced sound.

SUMMARY OF THE INVENTION In accordance with the invention, an improved sur- BRIEF DESCRIPTION OF THE DRAWINGS The nature and characteristic features of the invention will be morereadily understood from the following description taken in connection with the accompanying drawings forming part thereof, in which:

FIG. 1 is a vertical sectional view of a loudspeaker having the surround of the invention incorporated therein.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now more particularly to the drawing, a loudspeaker is there illustrated of the character disclosed in copending applications Ser. Nos. 864,320 and 864,321, filed Oct. 7, 1969 and Ser. No. 870,037, filed Oct. 28, 1969, all now abandoned.

The loudspeaker illustrated includes a rigid front ring connected by frame bars 11 to a rear frame plate 12.

The rear plate 12 has a permanent magnet structure 18 secured thereto, such as by screws 19. The magnet assembly also includes a core 20, spaced to provide a flux gap 21.

A voice coil 25 is provided extending in the gap 21 and is secured to the diaphragm or cone in driving relation thereto. Spaced coaxial supports 26 and 27 are employed to support the coil 25 and the said supports 26 and 27 are held by ring 29 carried on bolts 32 in the frame plate 12.

In accordance with the invention a surround 22 is provided in the form of a flat ring and which is of a stabilized closed pore foam elastomer, preferably of a bubble size half that of the thickness of the surround and no greater than percent of that thickness. The surround foamed material may be of rubber, natural or synthetic, including Neoprene, or of a silicone rubber or of a fluoro-elastomer available under the name Viton from E. I. du Pont de Nemours & Co., Wilmington, Delaware. The elastomer must be omni-directional in tension and those just mentioned have the desired characteristics. Foams of polystyrene and polyurethane which are more taut in one direction than in another are not suitable.

One particularly suitable material is sliced silicone rubber foam cut from the full blown inner parts of a sheet, and of a thickness of the order of twenty to thirty thousandths of an inch, the outer skins of which have been removed. Such silicone rubber has good qualities of extendibility or stretch, and recovery, and long life.

The surround 22 is preferably held in place by a mounting ring 16 and screws 17.

The surround 22, made of an elastomer as previously described, has the desired damping qualities and flexibility, particularly when the coil 25 mounted on the supports 26 and 27 is caused to oscillate. The supports 26 and 27 have high radial rigidity and high axial flexibility so that the surround 22 serves no supporting function and acts primarilyas an air separator at the periphery 14 of the diaphragm 15. For each inch of free surround material subject to stretch, about one inch or more of axial excursion will be accommodated without introducing sound distortion strains on the cone.

The surround 22 is very light and thin and, by its damping properties, damps out reflections from the frame ring 10 which could cause standing waves and undesired resonances.

The stresses at the edge of the cone 15 are relieved so that no cone break-up occurs. The break-up action in cones is discussed by Olson,'Acoustical Engineering, Published 1964 by D. Van Nostrand Co.

The break-up occurs when the linear elastic limit of the cone is exceeded by high stress, at which time the cones break into non-linear oscillations which produce distortion harmonics and in certain cases such harmonic distortion as well.

The break-up is a very serious limitation inhigh powered small cone loudspeakers of diameters of the order of six inches indiameter.

Because low frequency excursions are subject to increased extension inversely to frequency, the low frequency roll-off should be designed in proportion to the size cone, the surround spring constant and applied low frequency power.

By using the double rear support system and a light highly damping low spring constant surround 22, the stresses which build up in conventional designs do not occur, and break-up may be avoided at high power levels.

I claim:

1. In a loudspeaker having a frame,

a speaker cone,

driving means for said cone in said frame, and

supporting means in said frame for said cone and said driving means and providing substantially the entire support therefor,

front to back air separation for said cone. 2. A loudspeaker as defined in claim 1 in-which said surround is in a flat non-stressed mode when'inactive and stretches to accommodate equally forward or backward motion substantially free from stress on the periphery of the cone.

UNITED STATES P TENT @FMCE CERTIFPCATE @F CGRREQHON Patent No- 3.7s7,oo4 paved October 23, 1973 Inventofls) Arthurf Liebs cher It is eert'ified that error appears inthe above-identified pater'lt and that said Letters Patentere hereby corrected as shown below:

The address of the patentee appearing on the fees of the patent should read- I 11.86 Hart Lane Hartsville, Pa. 18974 Signed and sealed this 19th day of February 1971 (SEAL) Attest: I I I I I I a I EDWARD M.FLET0HER, JR. C MARSHALL DANN Attesting. Officer ,j

- Commissioner of Patents F ORM PC3-1050 1'0-69) USCOMM-DC 60376-1 69 s 0.5. sovammzn'r PRINTING ornc: was o-asa-su,

UNITED STATES PATENT OFFICE @ERTIF'ICAT-E 0F CQRRECTION Pat nt N 3,767,004 ated October 23, 1973 Inventofls) AJt'thur Lielescher I It is certified that error appears in the above-identified pater'lt and that said Letters Patentgare hereby corrected as shown below:

The address of the patentee appearing on the fece of the patent should read- 1186 Hart Lane Hartsville, Pa. 18974 Signed and sealed this 19th day of February 197L (SEAL) Attest: H v EDWARD M.FLETGHER,JR. c.' MARSHALL DANN Attesting Officer l Commissioner of Patents FORM PC4050 (TO-69) USCOMM-Dc 90376.p59

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1. In a loudspeaker having a frame, a speaker cone, driving means for said cone in said frame, and supporting means in said frame for said cone and said driving means and providing substantially the entire support therefor, the improvement which comprises a thin surround of stabilized impervious closed pore silicone rubber foam characterized by omni-directional elastic tension secured to the periphery of the cone and to said frame, said surround being disposed in non-supporting and non-stressing relation to said cone and providing front to back air separation for said cone.
 2. A loudspeaker as defined in claim 1 in which said surround is in a flat non-stressed mode when inactive and stretches to accommodate equally forward or backward motion substantially free from stress on the periphery of the cone. 